package com.lagou.sqlSession;

import com.lagou.config.BoundSql;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.utils.GenericTokenParser;
import com.lagou.utils.ParameterMapping;
import com.lagou.utils.ParameterMappingTokenHandler;
import com.lagou.utils.TokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * @author cheng
 * @since 2021/7/4
 */
public class SimpleExecutor implements Executor {

    public PreparedStatement prepare(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        // 1.注册驱动，获取连接
        Connection connection = configuration.getDataSource().getConnection();

        // 2.获取sql语句  select * from user where id = #{id} and username = #{username}
        // 转换sql语句  select * from user where id = ? and username = ?，转换过程中，还需要对#{}里的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象，prepareStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4.设置参数
        //   获取到了参数的全路径
        String paramterType = mappedStatement.getParamterType();
        Class<?> paramterTypeClass = getClassType(paramterType);
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            // 参数
            String content = parameterMapping.getContent();
            // 反射
            Field declaredField = paramterTypeClass.getDeclaredField(content);
            // 设置暴力访问
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);

            preparedStatement.setObject(i + 1, o);
        }

        return preparedStatement;
    }

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {

        // 调用设置过的预处理对象
        PreparedStatement preparedStatement = prepare(configuration, mappedStatement, params);

        // 5.执行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);
        ArrayList<Object> objects = new ArrayList<>();

        // 6.封装返回结果集
        while (resultSet.next()) {
            Object o = resultTypeClass.newInstance();
            // 元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            // metaData.getColumnCount():数据库中列的个数
            for (int i = 1; i <= metaData.getColumnCount(); i++) {
                // 字段名
                String columnName = metaData.getColumnName(i);
                // 字段的值
                Object value = resultSet.getObject(columnName);
                // 使用反射或者内省，根据数据库表和实体的对应关系，完成封装
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o, value);
            }
            objects.add(o);
        }
        return (List<E>) objects;


    }

    @Override
    public Integer update(Configuration configuration, MappedStatement mappedStatement, Object[] params) throws Exception {

        // 调用设置过的预处理对象
        PreparedStatement preparedStatement = prepare(configuration, mappedStatement, params);

        // 5.执行sql
        Integer updateNum = preparedStatement.executeUpdate();
        return updateNum;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {

        if (paramterType != null) {
            Class<?> aClass = Class.forName(paramterType);
            return aClass;
        }
        return null;
    }

    /**
     * 对#{}的解析工作：1.将#{}使用?进行代替，2.解析出#{}里面的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        // 解析出来的sql
        String parseSql = genericTokenParser.parse(sql);
        // #{}里面解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
        return boundSql;
    }
}
